Add function to create index from test rules folders

Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>

Author: AyanSinhaMahapatra

src/licensedcode/cache.py

@@ -138,6 +138,40 @@ def load_or_build(
             raise
 
 
+class MockCacheFromTestRules(LicenseCache):
+
+    @staticmethod
+    def build_from_test_rules(test_rules_dir):
+
+        from licensedcode.models import licenses_data_dir as ldd
+        from licensedcode.models import load_licenses
+
+        licenses_data_dir = licenses_data_dir or ldd
+        rules_data_dir = test_rules_dir
+
+        licenses_db = load_licenses(licenses_data_dir=licenses_data_dir)
+
+        index = build_index(
+            licenses_db=licenses_db,
+            licenses_data_dir=licenses_data_dir,
+            rules_data_dir=rules_data_dir,
+        )
+
+        spdx_symbols = build_spdx_symbols(licenses_db=licenses_db)
+        unknown_spdx_symbol = build_unknown_spdx_symbol(licenses_db=licenses_db)
+        licensing = build_licensing(licenses_db=licenses_db)
+
+        license_cache = LicenseCache(
+            db=licenses_db,
+            index=index,
+            licensing=licensing,
+            spdx_symbols=spdx_symbols,
+            unknown_spdx_symbol=unknown_spdx_symbol,
+        )
+
+        return license_cache
+
+
 def build_index(
     licenses_db=None,
     licenses_data_dir=None,
@@ -353,6 +387,14 @@ def get_index(force=False, index_all_languages=False):
     return get_cache(force=force, index_all_languages=index_all_languages).index
 
 
+def get_index_with_test_rules(test_rules_dir):
+    """
+    Return and eventually build and cache a LicenseIndex from a directory with
+    a few test rules for a specific test.
+    """
+    return MockCacheFromTestRules.build_from_test_rules(test_rules_dir).index
+
+
 get_cached_index = get_index